|  | 1.5 | Routing and the Different Classes of Routing Protocols
| 1.5.1 | Routing in a mixed LAN-media environment
The network layer must relate to and interface with various lower layers. Routers must be capable of seamlessly handling packets encapsulated into different lower level frames without changing the packets' Layer 3 addressing. The figure shows an example of this using LAN-to-LAN routing. In this example, packet traffic from Host 4 on Ethernet Network 1 needs a path to Host 5 on Network 2. When the router checks its routing table entries, it discovers that the best path to Network 2 uses outgoing Port To0, the interface to a Token Ring LAN. Although the lower layer framing must change as the router switches packet traffic from Ethernet on Network 1 to Token Ring on Network 2, the Layer 3 addressing for source and destination remains the same. The destination address remains Network 2, Host 5, despite the different lower layer encapsulations.